1. Field of the Invention
This invention relates to a tape cartridge in which a pair of tape reels each having wound thereon a tape-shaped medium such as a magnetic tape are housed within the inside of a man cartridge body portion and in which a metallic plate is insert-molded on a lower cartridge half constituting the main cartridge body portion.
2. Description of the Related Art
In general, in a conventional tape cartridge for a video tape recorder or DAT, a main cartridge body portion is formed by a lower cartridge half and an upper cartridge half each in the form of a shallow rectangular saucer opened on its front side. Within this main cartridge body portion are rotatably housed a pair of tape reels having wound thereon a magnetic tape, while a loading spacing is defined on the open front side. When the tape cartridge is loaded on a loading unit of a recording/reproducing apparatus, tape loading means provided on the recording/reproducing apparatus is intruded into this loading spacing. This loading spacing is opened or closed by a lid rotatably supported by the main cartridge body portion.
Meanwhile, such tape cartridge is known in which a metallic base plate is insert-molded in unison on a bottom surface of a lower cartridge half constituting the main cartridge body portion. This tape cartridge, having the base plate, is improved in mechanical strength against warping or torsion, while being increased in overall weight. If vibrations of a tape driving mechanism driving tape reels are applied to the tape cartridge, there is no risk of the tape cartridge being oscillated to affect the running of the magnetic tape, thus assuring high-precision recording/reproduction of information signals.
In a lower cartridge half 104, making up the tape cartridge, shown in FIG. 1A, a base plate 106 may be deemed to be substantially rigid with respect to a resin material when the lower cartridge half is thermally contracted following injection molding, so that the amount of contraction of the portion of a resin part 116 neighboring to the base plate 106 is substantially zero. On the other hand, the portion of the resin part 116 remote from the base plate 106 is contracted significantly, on thermal contraction following injection molding, as compared to the portion thereof neighboring the base plate 106.
That is, when the base plate 106 is insert-molded on the lower cartridge half 104, the portion of the lower cartridge half neighboring to the base plate 106 undergoes only small contraction, while the portion thereof remote from the base plate 106 undergoes significant contraction. The result is that the lower cartridge half 104 is subjected to tension in the longitudinal direction of the outer peripheral wall section due to such differential contraction as indicated by arrow in FIG. 2A. Thus the lower cartridge half 104 undergoes warping in its entirety as indicated in FIG. 2B. Such warping in the entire cartridge half is produced significantly in particular in the longitudinal direction of the lower cartridge half 104.